Sulfur removal from carbonaceous solids



United States Patent 3,115,426 8U REMQVAL FTGM CARBGNAEOUS SOLIDS IWilliam '3. Tolanrl, San Ralael, tlalili, assignor to (Iain forniaResearch Qorporatlon, San Francisco, Calltl, a corporation of DelawareNo Drawing. Filed May 2.6, H69, Ser. No. 31,794 12 Claims. (Cl. 134-3ii)This invention relates to a process for removing sulfur fromsulfur-containing carbonaceous solids including sulfocarbon-type reactordeposits, and for weakening and removing said deposits from equipmentwherein they are located.

In certain refinery and chemical processes, it is known that reactorfouling caused by steady accumulations of sulfur-containing carbonaceousreactor deposits imposes severe limitations on process operation,results in appreciable volume loss in expensive reactors, increasespressure drop, and is extremely detrimental in other significantrespects.

The sulfur-containing carbonaceous solids referred to herein includegenerally all carbonaceous solids c0ntaining sulfur; however, theprocess of the present invention is particularly valuable in removingfrom equipment deposits of the types of sulfur-containing carbonaceoussolids known as sulfocarbons. Sulfocarbons are well known in the art.For certain purposes other than as equipment deposits sulfocaroons haveutility in themselves, and are manufactured especially for these uses.The chemical composition, characteristics and methods of preparation ofvarious sulfocarbons are disclosed in various United States patents, forexample Gamson US. Patents 2,447,005, 2,447,606, 2,525,343, 2,539,187,2,539,188 and 2,569,095. These patents indicate that the sulfocarbonswith which they are particularly concerned have carbon contents rangingfrom 47 to 90 weight percent, sulfur contents ranging from 6 to 50weight percent, hydrogen contents ranging from .1 to 4 weight percent,and contain minor amounts of such other constituents as oxygen and ash.The patents indicate that the suitecarbons with which they are concernedcomprise sulfur, carbon and hydrogen in chemical combination. Wheresulfocarbons of the type referred to in the patents occur as deposits inequipment, they can be readily removed by the process of the presentinvention, pursuant to which the sulfocarbons are weakened by removal ofsulfur therefrom and thus are rendered amenable to physical destruction.

"requently, sulfocarbon-type equipment deposits resulting from sustainedoperation of various items of equipment in the chemical processindustries contain even higher percentages of sulfur than thesulfocarbons with which the aforementioned patents are concerned. Forexample, it has been found that sulfocarbon-type deposits in reactors inisophthalic plants of the type discussed hereinafter sometimes containup to about 85 weight percent sulfur, together with around 1 weightpercent hydrogen, the balance mainly consisting of carbon. However, alarge amount of tune sulfur content of these deposits often more than 50weight percent of the sulfur contentfrequently is in the form of freesulfur, with the remainder being combined sulfur as in the sulfocarbonsreferred to in the patents hereinabove discussed. The remaining combinedsulfur therefore often is present in approximately the same amounts asin the cited patents. The process of the present invention has beenfound to be effective in removing from the sulfocarbon-type depositslarge amounts of both free and combined sulfur.

it is well known that the sulfocarbon-type deposits referred to aboveare extremely difiicult to cope with in that they are insoluble andintractable, and when de- "ice posited in reactors during processoperation cannot be removed in order to restore reactor volume andefficient process operation by methods known heretofore, except by plantshut-down, equipment dismantling, and manual destruction or" the solidsmasses.

in View of the foregoing, it would be desirable if a simple andeflicient process were available for removing sulfocarbon-type reactordeposits in a minimum period of time Without the necessity for reactordismantling or prolonged plant shut-down.

The foregoing desirable objects are fully obtainable with the process ofthe present invention, as will be described in more detail below.Sulfocaroomtype reactor deposits may be treated by the process of thepresent invention to place them in a more readily transportable form.The reactor deposits are changed in composition and structure in amanner that removes a portion of them in a gaseous form and renders theremaining portion amenable to easy physical removal by subsequentprocess steps.

in accordance with the present invention, there is provided a processfor removing sulfur from sulfur-containing carbonaceous solids bycontacting said solids with hydrogen in the presence of a materialselected from the group consisting of water and hydrocarbons. Further,in accordance with the present invention, sulfur is removed fromsulfur-containing carbonaceous solid reactor deposits built duringnormal operation of a reactor which comprises disce n" luing normaloperation of said reactor and contacting said deposits in said reactorwith hydrogen and the water and/ or hydrocarbons. Still further, inaccordance with the present invention, the process desirably is carriedout at an elevated temperature and pressure and, when applied to reactordeposit removal, at least two cycles of alternate pressure steaming anddepressuring of said reactor desirably applied to the reactor depositsfollowing contacting of said deposits with said material and hydrogen.

The reactor deposit removal as, set of the present invention may bebetter understood from the following description of a specificembodiment of the invention, namely, the removal of sulfocarbon-typedeposits from a reactor in a plant for producing isophthalic acid.Recent processes have been developed for producing isophthalic acidwhich involve oxidation of Xylenes by an oxidizing medium comprisingsulfur or a sulfur species. Examples of such oxidations include: (a)sulfate oxidation of a xylene using an aqueous ammon um sulfateoxidizing medium and a hydrogen sulfide reaction initiator to producethe corresponding phthalic acid as disclosed, for example, in US. Patent2,722,549; (5)) sulfur oxidation of a xylene using sulfur and water toproduce t corresponding phthalic acid, as disclosed in U .8. Patent2,903,480; and (c) sulfur-ammonia oxidation of a xylene using sulfur andammonia to produce the corresponding phthalic acid, as disclosed in US.Patent 2,610,980. The foregoing reactions and other similar oxidationprocesses employ reaction mechanisms that inevitably result in theproduction of various by-products, for example, thioacids sulfurcompounds, that enter into side reactions, such as polymerization,reading to the production of heavy deposits of snlfocarbons on reactorinteriors. Such deposits build up in a steady accumulation duringreactor operation and seriously reduce reactor volume, disturb pressurebalances, and reduce reactor efficiency. These insoluble and intractabledeposits heretofore have resisted all etforts at their removal otherthan use of the most drastic expedients such as plant shut-down forprolonged periods of time, reactor dismantling, and chiseling out of thedeposits.

In accordance with the present invention, the reactor deposits referredto in the preceding paragraph may be removed simply, quickly, andefficiently at low cost. The foliowmg example illustrates a specificembodiment of the process of the invention.

EXAMPLE 1 A commercial isophthalic acid plant reactor having an originalvolume of about 700 cubic feet and containing suliiocarbon depositsbuilt up by steady accumulation durin sulfate oxidation of xylenes tophthalic acids was de- 1;

termined by tests to contain sufficient sulfocarbon deposits, amountingto thousands of pounds, to have reduced the reactor volume by over 35%from the original volume at the beginning of process operation. Processoperation was discontinued and the sulfocarbon deposits in the reactorwere subjected to a treatment with a combination of water and a gascomprising 75 volume percent f/drognen rat a temperature of 640 F. and3000 p.s.i.g. for a period of only 40 hours, the water being supplied 0the reactor during this period at a rate ranging from 1000 to 2500barrels per day and the gas being supplied to the reactor during thisperiod at a rate of from about 50 to 165 standard cubic feet per minute.It was found that operation under these conditions produced a reactioninvolving the sulfocarbon deposits and the feed Water and the gas thatresulted in a reactor off-gas containing unreacted hydrogen, and largequantities of hydrogen sul- Analyses of the off-gas showed that duringthe 40- hour period almost 2000 pounds of sulfur had been removed fromthe reactor deposits in the form of hydrogen fsulfide. This correspondedto about 15 of the calculated amount of sulfocarbon in the reactor.Following the 40-hour period, the reactor was cyclically subjected tosteam at 500 p.s.i.g. followed by rapid depressuring.

Such an operation would have had little or no effect on }ihet'ou-gh,insoluble and intractable sul-focarbons comprisi-in'g the originalreactor deposits prior to the water and hytirogen treatment; however,after the water and hydrogen treatment had been per-formed, it was foundthat the alternate high pressure steam and depressuring operationsflushed from the reactor amazingly large quantities of a powdery blacksolid material. This material was a substantial proportion of theremaining sulfocarbon deposit that had been made fragile and amenable tophysical removal by virtue of the sulfur removal accomplished during thehydrogen and water treatment. The combined hydrogen and water treatmentand the alternate high pressure steam and depressuring operationsresulted in reducing the unavailable reactor volume space occupied bysulfocarb'on-type deposits from 37% of the total to 1.5% of the total, ahighly surprising and unexpected result in View of the long-standingreactor deposit problem in the industry, in view of the relativesimplicity of the process used in the example.

Those skilled in the art will realize that many plant conditions andoperating factors such as the type of process leading to the deposits,the duration of process operation before deposit removal, the reactorsize, etc., will influence the optimum operating conditions for theprocess of the present invention, including water and gas feed rates,reaction tempenature and pressure and steam pressure applicable to theprocess. However, with the foregoing specific embodiment in mind andwith the follow- :ing remarks, those skilled in the art will be able todetermine with relative ease the necessary conditions under which thepresent process should be operated in their own situations. Generallyspeaking, it is prefenable that the water and hydrogen treatment of thesolid reactor deposits be conducted at from about 500 to 1000 F. andfrom about 1500 to 5000 p.s.i.g. The amounts of hydrogen and waterrequired for satisfactory results depends upon the composition andextent of the deposits, upon the treating tempenature and pressure andupon the time of treatment. For deposits in commercial plant reactorssuch as the isophthalic plant referred to herein, the deposit removalprocess preferably is conducted as a con- .tinuQuS operation at a waterfeed rate of 0.5 to 10 barrels per day per cubic foot of originalreactor volume and a hydrogen feed rate, based on hydrogen, of 0.01 to1.0 standard cubic foot per minute per cubic foot of original reactorvolume. It is clear that these figures are guides only and that a manskilled in the art being aware by the present disclosure of theunexpected efficacy of the present process and the advantages derivabletherefrom may operate within the above ranges or may possibly find thatoperation outside some of those ranges may be expedient for hisparticular situation.

Variations on the foregoing process are possible. For example, it may bedesirable in some situations to conduct the water and hydrogen treatmentportion of the process with the water in liquid phase, while in othersituations vapor phase may be desirable. In other situations, it may bedesirable to begin the operation Wit the water in liquid phase and,following a partial removal of sulfur from the reactor deposits, tocomplete the operation with the Water in vapor phase. In thisconnection, it has been noted that a relatively high reaction rate, asdetermined by analyses of the reactor off-gas, may be expected duringthe initial stages of the process, probably because of more rapidreaction of the free sulfur in the deposits. Following the reaction ofthe free sulfur, the water and hydrogen can more vigorously attack thecombined sulfur in the deposits, upon which the deposits begin to weakenwith the attendant danger that with water in liquid phase portions ofthe weakened deposits may break away and be carried with the water intoequipment piping. Such a happening might necessitate shutdowns if thedeposit portions plug the lines. Accordingly, a particularly desirableoperation would be one wherein the initial stage of the water andhydrogen treatment is conducted with the water in liquid phase until thefree sulfur in the deposits has been removed, after which the remainingtreatment is conducted with the water in vapor phase. A particularlydesirable combination of hydrogen and water feed rates to the process isone in which the hydrogen feed rate will be just enough to saturate thewater with hydrogen at operating temperature and pressure.

While the precise duration of the water and hydrogen treatment step mayvary widely, those skilled in the art will easily be able to determinewhen the treatment has progressed sufiiciently for their purposes, forexample, by making a continuous analysis of the reactor off-gas.

The examples in the following table will serve to further illustrate theprocess of the present invention. In each of the examples thesulfocarbon used was obtained from commercial isophthalic acid plantreactors and subjected to treatment pursuant to the process of thepresent invention in controlled batch-type laboratory runs.

Table 1 Example 2 3 4 5 6 Charge:

Suliocarbon, Wt. 53,--

From Reactor A 50 12.5 12.5 12. 5 12. 5 From Reactor B 5O 12. 5 12. 512. 5 12. 5 Composition, percent:

0 16. 3 13. 3 16. 3 16. 3 13. 3 IL. 11 1.1 1.1 1.1 1.1 S 82. 3 82. 382.3 82. 3 82. 3 Water, cc- 1.000 1.000 None 500 50 Xylene, cc- NoneNone 1, 000 500 None Hydrogen cold 1,000 750 700 700 650 Conditions:

Temperature. F. 630-40 630-40 640-50 635-40 640 Pressure, max. p 4, 0253, 725 1, 825 3, 700 2, 600 Time, min 70 1 180 Products:

Sulfocarbon, Wt. g 21. 5 4. 2 4. 2 2. 4 4. 8 Composition, Percent G 52.2 43. 0 51. 5 33. (l H 2. 5 1. 6 2.0 1.3 S 37. 0 32. 5 34. 7 32. 0 Ash36. 3 Calculations:

Percent Sultocarbon Removed 78. 5 83. 2 83. 2 90. 4 80. 9

From the above table it may be seen that by the process of the presentinvention, not only was free sulfur removed from the sulfocarbon-typedeposits, but also carbon, hydrogen, and some combined sulfur. Forinstance, in run 3 of the total sulfocarbon charged, 56% of the carbondisappeared, 76% of the hydrogen, and 93% of the sulfur. Where thehighest portions of sulfocarbon were removed, the ash content of theresidue became greater. For example, in run 5, the residue contained36.3% ash. In most cases a white solid sublimed from the residues whichwas proven to be thianthrene. In run 6, where the vapor phase waswithdrawn from the reactor at reaction temperature, this thianthrenecondensed in the H 5 scrubber. it represented up to perhaps of theresidue. Gaseous products consisted largely of hydrogen and hydrogensulfide.

The pressure of hydrogen used in the process of the present inventiondoes not appear to be particularly critical. This is borne out by theexamples in Table 1, above, in which the amount of residue obtained wasrelatively consistent over a wide range or" hydrogen pressure. Recyclingof residue with fresh hydrogen failed to decrease the weight of theresidue appreciably.

While water is the preferred medium for use with the hydrogen in theprocess of the present invention, mainly because of its availability andlow cost, hydrocarbons that are substantially inert under the conditionsused in the process may be used in lieu of water or in conjunction withwater. The hydrocarbons tend to have a useful solubilizing effect on thesulfur contained in the sulfocarbons; the xylenes are examples ofhydrocarbons that are especially effective in this regard. It will benoted from the above table that xylene was used instead of water inExample 4 and in that example 83.2% of the sulfocarbon was removed.

Hydrocarbons are useful in the process not only because of theirsolubilizing effect on the sulfur contained in the sulfocarbons, butbecause they tend to act as swelling agents for one or more of theconstituents of the sulfocarbons, and thus facilitate the loosening ofthe sulfocarbons from equipment and facilitate the weakening of thesulfocarbons themselves. Water is useful in the process not only becauseof its solubilizing effect on the sulfur contained in the sulfocarbons,but because it tends to hydrolyze some of the sulfur compounds presentin the sul-focarbons, thereby further aiding in weakening thesulfocarbons. Both water and hydrocarbons have utility in the process ascarrier media for transporting portions of the dislodged sul'focarbondeposits and materials removed from the deposits.

Examples of hydrocarbons that may be used alone or in combination in thepresent process include normally liquid and normally gaseous paraffins,aromatics and naphthenes, including pentane, butane, cyclohexane, thexylenes, benzene, toluene and deoalin, as well as petro leum distillatecuts, all other functionally equivalent hydrooarbons that are inertunder the conditions of the process, and combinations of the foregoing.Whether the foregoing hydrocarbons are used alone or in combination,water may be present in any proportion. Where hydro carbons are used inlieu of Water or in conjunction with water, normally liquidhydrocarbons, and preferably the aromatic hydrocarbons, are mostpreferred.

I claim:

1. A process for removing sulfiur from sulfur-containing carbonaceoussolids, which comprises contacting said material with hydrogen in thepresence of a material selected from the group consisting of water andinert normally liquid hydrocarbons at an elevated tempenature andpressure.

2. A process for removing sulfur from a sulfur-containing carbonaceoussolid, which comprises contacting said solid with hydrogen in thepresence of water at an elevated temperature and pressure.

3. A process as described in claim 2, wherein said water is in the vaporphase during said contacting.

4. A process for removing sulfur from sulfur-containing carbonaceoussolid reactor deposits built up during normal operation of a reactor,which comprises discontinuing normal operation of said reactor, andcontacting said deposits in said reactor with hydrogen and a materialselected from the group consisting of water and inert normally liquidhydrocarbons at an elevated temperature and pressure.

5. A process for removing sulfur from carbon-contalining reactordeposits built up during normal operation of a reactor, which comprisesdiscontinuing normal operation of said reactor, contacting said depositsin said reactor With water and hydrogen with at least a portion of saidwater in liquid phase until a substantial proportion of sulfur has beenremoved from said deposits, adjusting the process conditions to forcesaid water into vapor phase, and continuing said contacting with saidwater in vapor phase until a further substantial proportion of so furhas been removed from said deposits.

6. A process as in claim 5, with the additional steps of at least twocycles of alternate pressure steaming and depressuring of said reactorfollowing contacting of said solids with water and hydrogen gas.

7. A process as in claim 6, carried out in the added presence of aninert normally liquid hydrocarbon.

8. A process for removing sulfur from carbon-containtiug reactordeposits built up during normal operation of a reactor, 'which comprisesdiscontinuing normal operation of said reactor, contacting said depositsin said reactor with an inert normally liquid hydrocarbon and hydrogenwith at least a pontion of said hydrocarbon in liquid phase until asubstantial proportion of sulfur has been removed from said deposits,adjusting the process conditions to force said hydrocarbon into vaporphase, and continuing said contacting with said hydrocarbon in vaporphase until a further substantial proportion of sulfur has een removedfrom said deposits.

9. A process as in claim 8, wherein said hydrocarbon is xylene.

10. A process as in claim 8, with the additional steps of at least twocycles of alternate pressure vaporizing and depressuning of said reactorfollowing contacting of said solids with said inert hydrocarbon andhydrogen gas.

11. A process for removing sulfur from a sulfur-containing carbonaceoussolid which comprises contacting said solid with hydrogen in thepresence of an inert normally liquid hydrocarbon at an elevatedtemperature and pressure.

12. A process as in claim 11, wherein said hydrocarbon is Xylene.

References Cited in the file of this patent UNITED STATES PATENTS1,722,211 Guiardino July 23, 1929 2,171,009 Rostin et a1 Aug. 29, 19392,380,340 Simpson July 10, 1945 2,423,157 Reiss July 1, 1947 2,619,434Kraus Nov. 25, 1952 2,892,738 Dobratz June 30, 1959 2,901,423 Herbert et'al Aug. 25, 1959 FOREIGN PATENTS 10,530 Denmark Feb. 7, 1908

1. A PROCESS FOR REMOVING SULFUR FROM SULFUR-CONTAINING CARBONACEOUSSOLIDS, WHICH COMPRISES CONTACTING SAID MATERIAL WITH HYDROGEN IN THEPRESENCE OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF WATER ANDINERT NORMALLY LIQUID HYDROCARBONS AT AN ELEVATED TEMPERATURE ANDPRESSURE.